Op amp

Discussion in 'General Electronics Chat' started by MURUGESAN K, Feb 4, 2014.

  1. MURUGESAN K

    Thread Starter New Member

    Jul 16, 2013
    5
    0
    Dear sir,

    I am using an Op Amp uA 741.

    I am having 2 Dc power supply unit(unit A,Unit B). I am giving +12V and -12 V (+Vcc,-Vcc) to the op amp by using power supply unit A, and i am using power supply unit B to give input (+v,-v) to the same op amp. Which supply unit's ground should i choose as reference to take output voltage?
     
    Last edited by a moderator: Feb 4, 2014
  2. LvW

    Active Member

    Jun 13, 2013
    674
    100
    How is it possible to use one single unit (in your case A) to feed +Vcc as well as -Vcc ?
    Of course, you must use A for +Vcc and B for -Vcc. Both supplies are to be referenced to ground. For the signal input you need, of course, another signal source (ac or dc).
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    This is the basic method of creating a split supply using two separate powers. In this case two batteries. But the setup is valid for your situation
    [​IMG]
     
  4. LvW

    Active Member

    Jun 13, 2013
    674
    100
    The diagram as given by t06afre reveals the critical point.
    Following this diagram, you now have a voltage of 18 Volts between both supply pins of the opamp.
    And now you can ask: Why not 12V as described in your question ?
    The important aspect is the ground connection in the middle of the total voltage.
    Your opamp must "know" where the common reference point is (called "ground") because the input signal must be referenced to such a common potential rail (ground).

    Of course, you can use one single supply voltage only - however, not BETWEEN both supply pins but between one of these pins and ground. In this case, the desired dc operating point (dc quiescent output voltage) must be again somewhere in the middle of this voltage. Thus, your output can swing - caused by an input signal - in both directions from this operatimg point.
    But you must know that in this case you need some additional provisions (bias circuitry) at the opamp input.
    My recommendation: Start an internet search with the keyword "single supply operation".
     
  5. MURUGESAN K

    Thread Starter New Member

    Jul 16, 2013
    5
    0
    It is a Dual output Dc power supply unit. Each supply unit having 3 terminals.

    1. +12 v out
    2. -12 v out
    3.Ground.

    My doubt is which ground( unit A's Ground or unit B's Ground ) should i choose while taking output from Op amp .
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    If your power supply is of a dual or split type supply. Like you describe in post #5. You will only need one of the latter supply to power your opamp circuit with +/- 12 volt. The output from the opamp should use ground as reference point.
     
  7. BobTPH

    Active Member

    Jun 5, 2013
    782
    114
    The grounds of the two supplies must be connected together.

    Bob
     
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